Diagnosis of Sugarcane yellow leaf virus in asymptomatic sugarcane by RT-PCR

Sugarcane yellow leaf virus (SCYLV) that causes yellow leaf disease (YLD) in sugarcane belongs to Polerovirus. The disease expression is commonly observed during 6 to 8 months stages of the crop and there is a need to diagnose the disease before the symptom appearance. We have standardized RT-PCR technique with a new set of primers to detect SCYLV in sugarcane in pre-symptomatic stages of YLD. During presymptomatic stage 33 of the 44 varieties studied tested positive to SCYLV in RT-PCR. During eighth month stage all the 44 varieties have shown characteristic disease symptoms and except one all of them tested positive to the virus in RT-PCR. The two RT-PCR assays performed separately during pre- and post-symptom expression stages in 44 varieties clearly revealed that most of the varieties have detectable level of the virus in asymptomatic stage. Expression of disease symptoms and presence of the virus in all the varieties except one very clearly indicated the severe virus infection in the tested varieties. The studies also proved the diagnostic efficiency of the new set of primers to detect SCYLV in asymptomatic plants.